Jupiter-Saturn Conjunction

Hurried Observations

An unusually close conjunction of Jupiter and Saturn happened after sunset on December 21st. In weeks leading up to this event both planets were moving west to east relative to the stars. Jupiter, nearer the Sun, moved eastward faster than Saturn. So Jupiter steadily caught up to Saturn, like a faster car moving to overtake a slower one from behind. Four days before minimum separation, on December 17th, I rushed outside and looked for the planets in the southwest after sunset. Clouds and overcast were forecast after the 17th, so I wanted to take advantage of clear skies. At 6:17 pm EST I saw the following view captured with a two second exposure on my tripod-mounted Samsung phone camera.

The overexposed crescent Moon is about a half degree, or 30 arc minutes in angular diameter. Compare the Moon's diameter with the separation of the planets which was about 26 arc minutes at the time. Jupiter was brighter than Saturn and closer to the tree tops. The picture above roughly approximates the naked eye view. I spent several minutes moving the camera around to block streetlights and Christmas lights on nearby houses.

On December 21st skies were overcast and cloudy all day. It seemed unlikely to clear for the close conjunction. Nevertheless, I popped outside at 5:50 pm to check the sky. What an unexpected surprise to find clouds dissolving in the southwest! Hastily grabbing a coat and camera, I rushed outside to take the following picture at 5:59.

At first glance Jupiter and Saturn, closest to tree tops, look like a single star, almost indistinguishable as separate objects. If you click on the image to view it at full size, you can barely see dimmer Saturn as a bump on the right side of bright Jupiter's disc. Three stars lined up above the planets are in the constellation, Capricornus.

I increased camera magnification slightly to zoom in a bit and moved the camera to block bright lights. You can see the Saturn "bump" more clearly in the next image, especially if you click on the image to view it in full size.

A bit more magnification produced the next image.

Finally, I zoomed in quite a bit to the point where image quality was significantly worse. This showed the separation better.

Jupiter and Saturn were only about 6.25 arc minutes apart here! They would easily have fit within the same field of a planetary imaging camera mounted on my 130mm refractor, but there wasn't enough time to set up the telescope with all the necessary equipment. Instead, I hurried inside to haul out by big 25X100 binoculars. The two planets were beautiful companions in the same binocular field of view! Jupiter's moons were visible there also.

 

Saturn and Jupiter regularly pass each other about once every 20 years, but they haven't passed this closely and favorably placed for viewing since the year 1226. Do they ever get close enough for Jupiter's disc to overlap, or occult, Saturn's disc? Yes, but the last one happened 8,000 years ago. During this 2020 conjunction Jupiter and Saturn were almost exactly on the same line of sight from Earth. Since they were also somewhat close to the Sun (which had set only about 70 minutes before), Earth, Sun, Jupiter, and Saturn, in that order, were all almost lined up together along a straight line!

Although it was partly cloudy most of the next day on December 22nd, the planets were still remarkably close together. By the time I saw clouds clearing it was, once again, too late to set up a telescope. I thought the planets were too low near the horizon to see from my backyard where neighboring houses would block the view, but I discovered the planets were actually visible between two houses. I took the following image at 5:51 pm.

The foreground fence and houses were illuminated by bright spotlights glaring from surrounding neighbors. Separation on December 22nd was about 10 arc minutes, still astoundingly close, less than half a full Moon's diameter! Compare this final image with the very first image above from December 17th. You can see how Jupiter moved from below Saturn on the 17th to slightly above Saturn on the 22nd.